The shielding material for shielding radioactive ray is a novel material which can effectively protect the human body from the radiation of harmful ray. The development and application of the shielding material for shielding radioactive ray developed with the development and application of the atomic energy industry and the nuclear technology. In recent years, the nuclear technology not only has been used in national defense construction, but also has permeated into various fields including industry, agriculture, medical treatment and the like, such as applications of nuclear electric power generation and isotopes in industry, medical assay, pharmacy and sealing of nuclear wastes. In the process of production application, how to prevent the harm of various rays generated by nuclear radiation on the human body has been an innegligible issue in the utilization of the nuclear technology.
Radioactive ray mainly include X ray, α ray, β ray, γ ray, neutron ray, proton ray and so on. Their penetrabilities are different. As α particles, β particles and protons have electric charges, when they interact with the atomic electric field of a protective substance, their energy will be decreased, and even a protective material with very small thickness can also completely block them. Therefore, concrete for shielding radioactive ray mainly shields the X ray, the γ ray and the neutron ray.
The X ray is a type of electromagnetic waves with very short wavelengths and great energy, the wavelengths (about 0.001 to 100 nanometers, the wavelengths of the X ray applied medically are approximately between 0.001 and 0.1 nanometers) of the X ray are shorter than the wavelength of visible light, and their photon energy is tens of thousands to hundreds of thousands of times greater than the photon energy of visible light. As the X ray have short wavelengths and great energy, when irradiating a substance, only part of the X ray will be absorbed by the substance, and most of the X ray will pass through via gaps between atoms, showing strong penetrability. The ability of the X ray in penetrating substances is related to the energy of X ray photons, and the shorter the wavelength of an X ray is and the greater the energy of the photons is, the stronger the penetrability is. The penetrability of the X ray is also related to substance densities, and by utilizing the property of differential absorption, substances with different densities can be differentiated.
The γ ray is a type of electromagnetic waves with high energy and high frequency, and has enormous penetrability. As they penetrate a protective substance, they can be absorbed gradually, but only when the protective substance exceeds a certain thickness can they be absorbed completely.
Neutrons are particles without electric charges in atomic nuclei, and a neutron ray is a neutron current composed of these neutrons without electric charges. According to the magnitude of energy and the velocity of motion, the neutrons are divided into slow neutrons, intermediate neutrons and fast neutrons, nuclei can only capture and absorb the slow neutrons, the rapid neutrons can only be decelerated by colliding with nuclei, but when the nuclei of certain substances collide with the neutrons, secondary γ ray will be generated. The intermediate neutrons can be decelerated by the nuclei of light elements, so that required energy is captured.
Radioactive rays generated by an atomic reactor and an accelerator are mainly the γ ray and the neutron ray. Sometimes, a small quantity of low energy X rays are generated, shielding materials for shielding radioactivity can easily shield the X rays. Therefore, the protection issues of the atomic reactor and the accelerator mainly boil down to the issue of protection against the γ ray and the neutron ray.
With regard to the γ ray, the higher the density of a substance is, the better the shielding property is. Almost all materials have certain shielding capabilities again the γ ray, but when a light atomic mass material with small density is adopted, the thickness of a shielding structure is required to be great, and as a result, the area and volume of a building are increased. As the effect of materials with high atomic mass, such as lead, zinc and steel, in protecting against the γ ray is high, a shielding structure can be made thin, but these materials are expensive.
With regard to fast neutron and intermediate neutron, not only heavy elements but also sufficient light elements are needed, it is best to contain a lot of water, that is because water contains the lightest element, hydrogen, and in this aspect, water has an excellent shielding effect; and with regard to slow neutron, it has to be considered to contain a material for absorbing or shielding the slow neutrons.
Ordinary concrete is a cheap and satisfactory shielding material for shielding radioactive ray, but it is low in density and the content of the bound water. Therefore, thickness needs to be increased when an ordinary concrete structure is adopted.
For radiation-shielding concrete, not only are high volumetric weight and high bound water content required, but also the concrete is required to have good homogeneity. The shrinkage of concrete structures should be minimum during construction and use, and defects, such as cavities and cracks, are not allowed to exist. Besides, the concrete is also required to have certain structural strength and fire resistance.
Therefore, for the defects of the prior art, it is necessary to propose a shielding material for shielding radioactive ray that is composed of light elements and heavy elements properly and has good mechanical properties, waterproofness and constructability. The material containing the light and heavy elements can be layered, or can be a uniform mixture.